Increased efficiency in modern engines has resulted from valve train mass reduction, (for lower friction losses and/or higher engine speeds), and from increasing the number of valves per cylinder. Direct acting valve arrangements, as in overhead cam engines are of particular current interest since they can limit the reciprocating elements to the valves and their associated valve lifters.
Design efforts to reduce lifter mass have involved the use of Ceramics, metal matrix composites and magnesium, as well as other materials. But the cost of such materials, the special processing and the extensive development and testing required to use them can cause these designs to be cost prohibitive.
This invention provides means to minimize valve lifter mass through changes in geometry not requiring special materials. The valve lifter preferably has a cam lobe contact surface that is approximately the width of or slightly wider than the width of an associated cam lobe. The contact surface may be extended longitudinally (usually in the direction of the cam sliding motion) as desired to allow high velocity cam profiles to be used without requiring an increase in the width of the contact surface or the lifter. Semi-cylindrical end walls or skirts depend from the longitudinal ends of the cam lobe contact surface to guide and stabilize the lifter in the lifter gallery. The walls may be ribbed for strength.
A circular recess in a mechanical version of the lifter is adapted to receive a valve shim. In a hydraulic version of the lifter, a cylindrical depending wall between the semi-cylindrical skirts defines a cylinder to receive a hydraulic lash adjuster. In preferred embodiments, low mass and adequate strength characteristics are provided by the use of thin walls and reinforcing ribs preferably formed by investment casting.
The invention further provides a valve lifter having an oblong cam engaging portion with spaced longitudinal ends connected with depending semi-cylindrical end walls for carrying both longitudinal and lateral side loads applied to the lifter.
In combination in an engine, the invention provides a lifter carrier having an opening including spaced semi-cylindrical end portions and a valve lifter as above described guidingly received therein.
These and other features of the invention will be more fully understood from the following description of certain preferred embodiments taken together with the accompanying drawings.